Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is cut or rolled into the material.
More common than knurl cutting, knurl rolling is usually accomplished using one or more very hard rollers that contain the reverse of the pattern to be imposed.
Rolled knurls are somewhat more complicated to design than cut knurls because the outer diameter of the work piece must be chosen to allow the roller to roll an integral number of patterns around the workpiece. By comparison, for cut knurls, the spacing of the cuts is not preset and can be adjusted to allow an integral number of patterns around the workpiece no matter what the diameter of the workpiece.
Hand knurling tools are available. These resemble pipecutters but contain knurling wheels rather than cutting wheels. Usually, three wheels are carried by the tool: two left-handed wheels and one right-handed wheel or vice versa.
Cut knurling often employs automatic feed, the tooling for cut knurling resembles that for form knurling with the exception that the knurls have sharp edges and are presented to the work at an angle allowing the sharp edges to cut the work, angled, diamond and straight knurling are all supported by cut knurling It is impossible to cut knurling "Like extremely coarse pitch threads" both because lathe gear trains will not support such longitudinal speeds and because reasonable cutting speeds would be impossible to achieve.
Tool handles, mechanical pencils, barbell bars, and the control knobs on electronic equipment are frequently knurled.
Knurling can also be used when a component will be assembled into a low precision component, for example a metal pin into a plastic molding. The outer surface of the metal pin is knurled so that the raised detail 'bites' into the plastic irrespective of whether the size of the hole in the plastic closely matches the diameter of the pin.